Additionally use version number in Lenny default pinning.

Additionally use version number in Lenny default pinning.

Lenny's APT does not support pinning like this:

  Pin: release o=Debian,n=<%= codename %>

We therefore switched (in commit ef2ebdffd) to:

  Pin: release o=Debian,a=<%= release %>

With such a pinning setup, when Squeeze is released, systems using this module
with $apt_use_next_release set to true would immediately switch to prefer
packages from Squeeze. If an automated upgrade process is setup, they would be
automatically upgraded to Squeeze.

This does not sound safe to me, so let's use the release version number as an
additional selection criterion to prevent upgrades to Squeeze to happen behind
our back:

  Pin: release o=Debian,a=<%= release %>,v=<%= release_version %>*

Note that the trailing '*' is intentional and necessary to match stable
point-releases.